[multi asic] Display the bgp mon session in the show ip bgp summary

[arlakshm]

What I did

The sonic-net/sonic-buildimage#6920 adds support of adding BGP monitor session on one of the backend ASICs of Multi ASIC platforms.
This PR enchances the show ip bgp summary command to display this session

Also added unit tests for 'show ip bgp summary' for multi asic platforms

How I did it

Change the bgp_run_command function to look at session of the all the namespaces.

How to verify it

Execute the command on Multi ASIC platforms

admin@sonic:~$ show ip bgp summary

IPv4 Unicast Summary:
asic0: BGP router identifier 10.1.0.32, local AS number 65100 vrf-id 0
BGP table version 12825
asic1: BGP router identifier 10.1.0.32, local AS number 65100 vrf-id 0
BGP table version 12011
asic2: BGP router identifier 10.1.0.32, local AS number 65100 vrf-id 0
BGP table version 12872
asic3: BGP router identifier 10.1.0.32, local AS number 65100 vrf-id 0
BGP table version 12904
asic4: BGP router identifier 8.0.0.4, local AS number 65100 vrf-id 0
BGP table version 12833
asic5: BGP router identifier 8.0.0.5, local AS number 65100 vrf-id 0
BGP table version 12833
RIB entries 77382, using 14238288 bytes of memory
Peers 41, using 857720 KiB of memory
Peer groups 21, using 1344 bytes of memory


Neighbhor      V     AS    MsgRcvd    MsgSent    TblVer    InQ    OutQ  Up/Down    State/PfxRcd    NeighborName
-----------  ---  -----  ---------  ---------  --------  -----  ------  ---------  --------------  --------------
10.0.0.1       4  65200       3196         77         0      0       0  00:06:15   6370            ARISTA01T2
10.0.0.5       4  65200       3196         74         0      0       0  00:06:15   6370            ARISTA03T2
10.0.0.9       4  65200       3196         55         0      0       0  00:06:17   6370            ARISTA05T2
10.0.0.13      4  65200       3196         55         0      0       0  00:06:17   6370            ARISTA07T2
10.0.0.33      4  64001         12       6415         0      0       0  00:06:18   33              ARISTA01T0
10.0.0.35      4  64002         12       6415         0      0       0  00:06:18   33              ARISTA02T0
10.0.0.37      4  64003         13       6415         0      0       0  00:06:18   34              ARISTA03T0
10.0.0.39      4  64004         12       6415         0      0       0  00:06:18   33              ARISTA04T0
10.0.0.41      4  64005         13       6415         0      0       0  00:06:18   34              ARISTA05T0
10.0.0.43      4  64006         12       6415         0      0       0  00:06:18   33              ARISTA06T0
10.0.0.45      4  64007         12       6415         0      0       0  00:06:18   33              ARISTA07T0
10.0.0.47      4  64008         12       6415         0      0       0  00:06:18   33              ARISTA08T0
10.0.0.49      4  64009         12       6415         0      0       0  00:06:18   33              ARISTA09T0
10.0.0.51      4  64010         12       6415         0      0       0  00:06:18   33              ARISTA10T0
10.0.0.53      4  64011         12       6416         0      0       0  00:06:19   33              ARISTA11T0
10.0.0.55      4  64012         12       6416         0      0       0  00:06:19   33              ARISTA12T0
10.0.0.57      4  64013         12       6416         0      0       0  00:06:19   33              ARISTA13T0
10.0.0.59      4  64014         12       6416         0      0       0  00:06:19   33              ARISTA14T0
10.0.0.61      4  64015         12       6416         0      0       0  00:06:19   33              ARISTA15T0
10.0.0.63      4  64016         12       6416         0      0       0  00:06:19   33              ARISTA16T0
10.0.0.65      4  64017         12       6416         0      0       0  00:06:19   33              ARISTA17T0
10.0.0.67      4  64018         12       6416         0      0       0  00:06:18   33              ARISTA18T0
10.0.0.69      4  64019         12       6416         0      0       0  00:06:19   33              ARISTA19T0
10.0.0.71      4  64020         12       6416         0      0       0  00:06:19   33              ARISTA20T0
25.171.16.3    4  65100          0          0         0      0       0  never      Connect         bgp_monitor

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[arlakshm]

/Azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[arlakshm]

/Azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).